12 research outputs found
Early-age monitoring of fresh cementitious material by acoustic emission
Concrete properties are mainly affected by the fresh state since it has a significant impact on the long-term concrete
performance. In this study, acoustic emission (AE) was applied to monitor the behavior of fresh cement paste. AE is
based on the detection of high-frequency elastic waves originating from different material sources. This highly
sensitive technique provides data that contribute to a deeper understanding of the different ongoing processes for fresh
concrete, as the possible AE sources are many. Characterization of each different source type is difficult and therefore,
a combined methodology of AE, capillary pressure in the matrix and specimen deformation was applied to monitor
the fresh cement paste
Monitoring early-age acoustic emission of cement paste and fly ash paste
In this study, a combined approach of several monitoring techniques was applied to allow correlations between the AE activity and related processes such as shrinkage and settlement evolution, capillary pressure and temperature development in fresh cementitious media. AE parameters related to frequency, energy, and cumulative activity which exhibit sensitivity to the particle size distribution of cement paste are compared with inert fly ash (FA) leading to isolation of the mechanical sources from the chemical ones. Characterization of the origin of different processes occurring in cement paste during hydration is complex. Although acoustic emission (AE) monitoring has been used before, a qualitative relation between the microstructural formation or other early-age processes and the number or parameters of AE signals has not been established. The high sensitivity of AE enables the recording of elastic waves within the cementitious material, allowing the detection of even low-intensity activities
Monitoring Acoustic Emission of Fresh Cement Paste
High strength and durability are the key factors determining the quality of concrete. To achieve the required properties, concrete mix design, and early age hydration, are the main factors affecting the performance of concrete. It is essential to monitor fresh concrete continuously through non-destructive techniques at the moment of mixing. In this study, acoustic emission (AE) has been applied to allow a continuous monitoring of the fresh cement paste. This non-destructive inspection allows the estimation of concrete properties by capturing elastic waves that are nucleated and propagate in the cement past. Moreover, ultrasonic pulse velocity (UPV), capillary pressure and heat evolution monitoring has been applied on cement paste to study the process of hydration mechanism. This study aims to check the sensitivity and effectiveness of AE technique to characterize the ongoing processes in fresh cementitious material and the possibility to contribute to a better monitoring of the process as an additional tool
Application of digital image correlation to cement paste
In this paper digital image correlation (DIC) has been applied to study the deformation
process of cementitious material at very early age. After mixing of cement-based materials, the
cement hydration process begins. Consequently, the ongoing Chemical reactions result in a 3D
deformation process (shrinkage). The mechanism affecting the very early age hydration as well as
specifically the deformation behavior of cementitious materials is a challenging topic. In view of
that, it is essential to determine the significant effect of concrete hardening process on the
deformation progression at different stages. The technique of DIC is highly sensitive and allows for
the first time in literature an accurate and non-contact optical monitoring of the shrinkage of fresh
cementitious material. The displacement of the surface is measured by correlating the different
digital images taken at different ages after mixing of the material. The system enables a 3D
observation that allows a deeper understanding of the deformation progression. The surface
displacement determined by DIC-software (Vic-Snap 2010) is compared to the displacement
measured by Linear variable differential transformer (LVDT) sensors for calibration purposes. DIC
system realizes a more precise method avoiding the effect of self-weight of the traditional sensor.
The purpose of this work is to check the sensitivity as well as the effectiveness of DIC technique, to
characterize and better understand the 3D deformation process of fresh cementitious materials
Monitoring the hydration of cementitious material by acoustic emission
Studying the mechanisms affecting the very early age hydration as well as the microstructure of
cementitious materials is essential to improve concrete performance. Consequently, it is necessary to monitor and
onderstand the early age hydration process.
In this work, continuous acoustic emission (AE), ultrasonic pulse velocity (UPV), and capillary pressure
monitoring has been applied on Consolidated and non-consolidated cement paste to study the process of hydration
mechanism as well as the formation of the microstructure.
Preliminary experiments have presented a large rate of AE activities in the fresh state. Ultrasonic tests exhibited
an increase of pulse velocity during hydration while capillary pressure and heat evolution were also monitored.
The purpose of this study is to verify the sensitivity of AE to follow the ongoing processes in fresh cementitious
material and the possibility to contribute to a better monitoring of the process as an additional tooi
Study on mechanical acoustic emission sources in fresh concrete
Acoustic emission testing has proven very useful as a non-invasive monitoring method for several material processes. Recently several studies have emerged related to fresh concrete monitoring, as AE has the sensitivity to record waves from many different processes, even though no external load is applied to the specimens. Due to the complexity of the activity including among others formation of hydrates, settlement, water migration, early age cracking, the accumulated AE cannot be easily explained. In the present paper, two mechanisms of mechanical origin (aggregate and bubble movement through the paste) are isolated and the characteristics of their emissions are studied. Experimental results are complemented with numerical simulations to enhance the understanding due to the complexity of the wave propagation problem. (C) 2017 Politechnika Wroclawska. Published by Elsevier Sp. z o.o. All rights reserved
Monitoring fresh cementitious material by digital image correlation (DIC)
Concrete undergoes strong displacements due to different processes at very early state, like
shrinkage. This early state of concrete affects the long-term concrete performance. The
concrete deformation cannot be directly attributed to a single process, due to the complexity
of different processes such as, evaporation, water migration, settlement, formation of
hydrates, shrinkage, early age cracking. Monitoring concrete properties at a very fresh state is
essential to understand the different ongoing processes. Digital image correlation (DIC) has
proven very useful as an optical and contactless method for surface monitoring of several
materials. In the present paper the displacement distribution of fresh cementitious material
from plastic state up to hardened state is studied by means of DIC. Moreover, an innovative
technique of speckle pattern creation is presented, since creation of a pattern on fresh (and
hence viscous) cementitious materials is not straightforward. The specimen surface is covered
with a speckle pattern that deforms together with the specimen. The principle of DIC realizes
a 3D continuous monitoring by recording the images at different time steps and comparing it
to the reference or undeformed image. The experimental results confirmed the effectiveness
and correctness of the new technique giving a global overview much more representative than
point measurements with traditional displacement meters
Fresh concrete monitoring by NDT techniques
The most reliable examination for concrete is mechanical testing (usually compression) after hardening.
However, ensuring the quality of fresh concrete before hardening, substantially reduces the possibility of
performance at standards lowerthan designed. Curing of conventional cementitious material is complicated
and becomes even more complicated considering the new generation of additives like super absorbent
polymers and nano-reinforcement which may strongly modify cement behaviour. In order to obtain better
control on the process from very early age, this study describes a combined approach of several monitoring
techniques. Acoustic emission (AE) is applied to record the sources occurring during the first hours when
concrete is still in liquid form and later when hardening takes place when shrinkage cracking occurs. In
addition, pressure sensors register the development of capillary pressure in the matrix and indicate the
moment of air entry into the System, which is the precursor of cracking. Settlement and shrinkage, measured
both non-contact by Digital Image Correlation (DIC) and conventionally, as well as temperature shed light
into the complex processes occurring into fresh concrete and help to verify the sources of AE. Among other,
mechanical sources like aggregate impacts due to gravity and air bubbles release are isolated and tested in
a dedicated experiment showing that these produce recordable AE despite the viscous nature of paste. The
final aim is to develop a methodology to assess the quality of the fresh concrete from an early age, to
possibly project to the final mechanical properties and to ensure a proper service life
Full-field settlement measurement at fresh cementitious material by digital image correlation
Monitoring concrete properties at a very fresh state is essential to understand the different ongoing processes. Concrete undergoes strong displacements due to different processes such as, evaporation, water migration, settlement, formation of hydrates, shrinkage, early age cracking. This early state of concrete affects the long-term concrete performance. In the present paper the displacement distribution of fresh cementitious material from plastic state up to hardened state is studied by means of the optical and contactless method of DIC. The principle of DIC realizes a full-field 3D continuous monitoring of the surface displacement. An innovative technique of speckle pattern creation allows monitoring the surface displacement few minutes after casting of cement paste and mortar. The experimental results confirmed the effectiveness and correctness of the new technique giving a global overview much more representative than point measurements with traditional displacement meters